Inspection systems are widely known for inspecting a pattern or the like which is formed on a surface of an inspection target object. In these inspection systems secondary charged particles which is obtained according to characteristic conditions of the surface of the inspection target object by irradiating a surface of an inspection target object such as a wafer with charged particles or electromagnetic waves are detected by an imaging unit, and the pattern or the like formed on the surface of the inspection target object is inspected by using image data generated based on the results of the detection (for example, refer to International Patent Publication No. 2002/001596, Japanese Patent Application Public Disclosure No. 2007-48686, and Japanese Patent Application Public Disclosure No. H11-132975). In many of these inspection systems, a form is adopted in which an inspection target object are irradiated with charged particles or electromagnetic waves while the traveling stage on which the inspection target object is held is caused to move and a quantity of light is taken in from an imaging unit every time the traveling stage moves a distance corresponding to one pixel of a captured image (an image captured by an imaging element) (a distance in which a traveling distance of an image projected on to the imaging element is one pixel and which is determined by the magnification of an optical system) to thereby generate image data. An example of a unit by which the size of one pixel of a captured image is expressed on an object surface of an imaging target object is nm/pix. In the case of one pixel corresponding to 50 nm on the object surface, it is expressed as 50 nm/pix. In this case, a stage traveling distance corresponding to one pixel is 50 nm. A timing at which the quantity of light is taken in is determined by a timing signal which is inputted into the imaging unit.
In this inspection system, in general, it is detected by using a laser interferometer that the traveling stage moves the distance corresponding to one pixel of the captured image. Specifically, it is determined whether or not the traveling stage has moved the distance corresponding to one pixel by converting a count value which is obtained from the laser interferometer as an integer value into an actual distance. For example, in the event that the resolution of the laser interferometer is 0.61815562 nm/count and the distance corresponding to one pixel is 50 nm, an accurate count value which corresponds to the distance corresponding to one pixel is 80.8858 counts (=50/0.61815562). However, as described above, the count value is obtained as an integer value. Because of this, in the conventional inspection systems, 81 counts, which results from rounding off a decimal part of the accurate count value (values below the decimal point), is treated as the distance corresponding to one pixel.